Abstract: In order to research the effect of ground temperature on gas occurrence in deep coal seam, the Langmuir equation is derived by thermodynamic theory based on the monolayer adsorption theory. The theory expressions between Langmuir constants (a and b) and temperature are also obtained. The coal and gas isothermal adsorption experiments are also carried out. Experimental results show that for given gas-solid adsorption system, the Langmuir constant a is determined by the intrinsic adsorption sites of adsorbent and depends on the adsorbent and corresponding adsorbate. Other factors such as environmental temperature and pressure have no effect on the value of a. The Langmuir constant a can be considered as a constant value for the same kind of coal. Langmuir constant b of different adsorbent is also different because of their nature physical properties. Langmuir constant b decreases with the increase of temperature. The experimental results correspond well with relations derived from the theory equations for Langmuir constants and temperature, which settles disputes about this issue existed for a long time. In engineering application, the relation between b and temperature can be described as a linear decreasing function for given temperature range.